Following are the reasons for all these variations:

• Battens are necessary to support that part of the sail area that we call "roach". This is sail area that is OUTSIDE a straight line between head and clew. Without battens to support this extra area, the "roach" would simply flop over to leeward and flap.

• On the otherhand, a "storm mainsail", with no roach, has no reason to have any battens.

• There is a limit to how big a roach (extra area) can be supported by non full length battens. Therefore if a bigger than usual roach is desired, full length battens should probably be considered, to support that roach.

• Full length battens, running from leech to luff, offer several benefits.

  a) they support the designed shape of the sail, helping to maintain this shape under a variety of wind conditions, loads, and sail trims. The benefit of this extra shape maintaining ability is more speed.

  b) They dramatically reduce the amount of "flogging" (flapping) that the sail experiences under hoisting, reefing and lowering. Since "flogging" weakens the sail material, it also shortens the effective longevity of the sail. So full battens prolong the life of the sail significantly.

  c) A fully battened mainsail will maintain its shape even when eased and twisted radically, without experiencing the flogging that a non full battened mainsail would have when trimmed this way. This means that with a fully battened mainsail, you have the option of "over twisting" and easing the main, to depower it. This can often equate to having taken a reef in the sail, but without the effort normally connected to that operation. This can be a significant bonus if sailing short handed.

Full length battens need some sort of batten fitting at the forward / luff end, often referred to as a "Luff Box". Pictured are a few non-adjustble options.

• The bigger the sail (longer leech, bigger roach etc.), the greater the number of battens used, and the longer they need to be, whether full length or partial.

• Battens come in a wide variety of materials, thicknesses, widths, weights and prices. It is best to match the appropriate battens for their intended use. Most sailmakers will supply the appropriate sized battens with your new sail.

• In small recreational dinghies, three short battens are often sufficient to support the moderate roach that is usual in these cases. Usually these battens will be perpendicular to the straight - line leech. Their length is related to the size of the roach. A sailmaking rule of thumb says that a batten should protrude twice as far into the sail (past the straight - line leech) as the amount of roach it has to support. Example: to support 6" of roach, use an 18" batten.

• Battens almost always divide the leech into equal segments. In other words, the distance between the battens is uniform, regardless of the number of battens used.

• Larger daysailers, and small to medium sized keelboats usually use four battens instead of three. This is the most common number of battens. Usually these are perpendicular to the straight - line leech. the exception to this is when there are one or more rows of reefing in the mainsail. In these cases, the bottom batten is often kicked up parallel to the lowest reef, making it easier to flake the batten into the reefed part of the sail.

• Full length battens are used to support a larger than normal roach. One full length batten is often used as the upper batten in one - design mainsail, not because the roach is big, but because the full length batten will help to maintain optimal sail shape near the top of the sail. The drawback is that a full length top batten is less easy to flake when the sail is lowered.

• When the roach is larger than normal, and / or you simply want the benefits (described in point 5) of full length battens, the usual number is four,. These will be evenly spaced, and will be approximately parallel to the sail foot, to aid in flaking the sail on the boom.

• With boats larger than about 40 ft., and with a large roach, the number of full length battens may be increased to 5, or even 6 if the boat is bigger still. This is because if the intervals between the battens become to large, some of the advantage of having the full length battens is lost.

• Another option is to combine partial and full length battens in the same sail. The reason for this would be to try to obtain most of the advantages of the full length battens throughout, but while saving both weight and money. The usual combination here is to use 2 full length battens in the upper half of the sail, and 2 partial (but longer than normal) battens in the lower half of the sail. This "compromise " solution works best in boats under 40 feet.

• Vertical battens, either partial or full length (leech down to foot) are used to support the roach of a mainsail that furls into the mast. If these are partial length, they must be considerably longer than had they been perpendicular to the straight - line leech, since the length of the batten does not project as far into the sail, given its angle.